Finding play testers has turned out to be the hardest thing for me to do in relation to game development.

Quality testers (those that will actually report bugs and be critical of game aspects) are very hard to find.

The only source I have found so far is to post on game forums. A large percentage of these will ban you, as developers posting about their game is considered spam by those sites. Even sites dedicated to indie games sometimes do this!

We really need a site dedicated to matching players who want to test games (they are out there) with developers.